Yii2: Your requirements could not be resolved to an installable set of packages.

[ishankhare07]

What steps will reproduce the problem?

General steps mentioned in Install via Composer
error comes on the php composer.phar create-project yiisoft/yii2-app-basic basic 2.0.9

What is the expected result?

What do you get instead?

Problem 1  

    - yiisoft/yii2 2.0.9 requires ext-mbstring * -> the requested PHP extension mbstring is missing from your system.  

    - yiisoft/yii2 2.0.8 requires ext-mbstring * -> the requested PHP extension mbstring is missing from your system.  

    - yiisoft/yii2 2.0.7 requires ext-mbstring * -> the requested PHP extension mbstring is missing from your system.  

    - yiisoft/yii2 2.0.6 requires ext-mbstring * -> the requested PHP extension mbstring is missing from your system.  

    - yiisoft/yii2 2.0.5 requires ext-mbstring * -> the requested PHP extension mbstring is missing from your system.  

    - Installation request for yiisoft/yii2 >=2.0.5 -> satisfiable by yiisoft/yii2[2.0.5, 2.0.6, 2.0.7, 2.0.8, 2.0.9].

Additional info

| Q | A |
| --- | --- |
| Yii version | 2 |
| PHP version | 7.0.8 |
| Operating system | Ubuntu 16.04 |

[samdark]

It says what's wrong:

the requested PHP extension mbstring is missing from your system.  

[LarryMarzanJr]

I solved this by installing the mbstring extension as @samdark said. Try installing this:

sudo apt-get install php7.0-mbstring